Fluid conveyance device

ABSTRACT

A fluid conveyance device includes a substrate, and a disk-shaped piezoelectric element arranged in a bendable manner on the substrate. A plurality of substantially circular concentric segment electrodes are provided on the piezoelectric element, and are provided with voltages with phases that are shifted. A wavy ring deformation is thus produced on the piezoelectric element. A pocket produced between the piezoelectric element and the substrate is moved in a radial direction so as to convey a fluid from an outer substantially circular portion to a central portion and to discharge the fluid from the central portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to fluid conveyance devices and, inparticular, to a fluid conveyance device utilizing a bendingpiezoelectric element.

2. Description of the Related Art

A piezoelectric pump has been used as a coolant water pump for a compactelectronic apparatus, such as a notebook personal computer, and a fueltransport pump for a fuel cell, for example. The piezoelectric pump isalso used as a fan pump which replaces a cooling fan for a CPU or otherelectronic apparatus, or a fan pump for supplying oxygen required by afuel cell that generates power. The piezoelectric pump is a pump thatutilizes a piezoelectric element that bends into a shape thereof inresponse to voltage application. The advantages of the piezoelectricpump are a simple and thin structure and low power consumption.

Japanese Unexamined Patent Application Publication No. 2-149778 andJapanese Unexamined Patent Application Publication No. 4-86388 disclosepiezoelectric pumps. In the piezoelectric pumps, a vibration plate isarranged in contact with a pump body having an inlet port and an outletport, and a plurality of piezoelectric elements are arranged from theinlet port to the outlet port on the vibration plate. In this pump, whenthe piezoelectric elements arranged from the inlet portion to the outletport are successively driven, the vibration plate is bent, one portionafter another, from the inlet port to the outlet port so that a fluid ispushed from the inlet port to the outlet port. When voltage applied tothe piezoelectric element stops, a flow passage between the inlet portand the outlet port is closed in response to a recovery of the vibrationplate. Therefore, a check valve between the inlet port and the outletport is not required.

In the above-described related art, the piezoelectric pump includes theplurality of bonded piezoelectric elements which have voltages that aredifferent in phases applied thereto, and thus, operates as a tube pumpwhich conveys a fluid from one end to the other end of the pump body.Since the plurality of piezoelectric elements are arranged in a plane,the pump has a bulky and complex structure. Since the plurality ofpiezoelectric elements operate in a tube-pump mode, the structure of anelastically deformable joint connecting the piezoelectric elements andsealing of the fluid presents difficulties. A mechanism for conveying aminiature volume pocket holding the fluid is also difficult toimplement.

Japanese Unexamined Patent Application Publication No. 1-500892discloses a fluid pump which includes ring segment electrodes providedon each of a central portion and a periphery portion of a piezoelectricelement. The central portion and the periphery portion are expanded andcontracted in opposite directions to bend the piezoelectric element andthus functions as a pump to convey a fluid. The piezoelectric element isrectangular, and segment electrodes are arranged in a longitudinaldirection of the piezoelectric element. In this case, the bending shapeof the piezoelectric element is also in a tube-pump mode in which thepiezoelectric element bends from one end to the other end. As in theabove-described related art, a plurality of electrodes must be arrangedin the direction of motion, and the pump has a bulky structure. Sealingof a joint connecting the elastically deformable electrodes is alsodifficult.

A miniature volume pocket containing the fluid is also difficult toconvey.

SUMMARY OF THE INVENTION

To overcome the problems described above, preferred embodiments of thepresent invention provide a simple and compact structure for a fluidconveyance device which efficiently conveys a fluid.

A preferred embodiment of the present invention provides a fluidconveyance device including a substrate, and a disk-shaped piezoelectricelement arranged on the substrate so as to be bendable. A plurality ofcircular or substantially circular concentric segment electrodes areprovided on the piezoelectric element. A voltage application unit isarranged to apply voltage to the segment electrodes with the voltagesuccessively being shifted in phase. The voltages are applied to thesegment electrodes with the phase thereof shifted to cause a wavy ringdeformation on the piezoelectric element and move a ring pocket causedbetween the piezoelectric element and the substrate in a radialdirection so that a fluid is conveyed between an outer substantiallycircular potion and a central portion of the substrate.

In accordance with a preferred embodiment of the present invention, thedisk-shaped piezoelectric element includes the plurality of circular orsubstantially circular concentric segment electrodes arranged on thesubstrate. The substrate and the piezoelectric element are preferably incontact with substantially no gap therebetween when no voltage isapplied to the piezoelectric element. When voltages having the same orsubstantially the same amplitude and shifted in phase are applied to thesegment electrodes, a wavy ring deformation occurs on the piezoelectricelement. The wavy ring deformation produces a ring pocket between thepiezoelectric element and the substrate. The ring pocket moves in aradial direction from the outer substantially circular portion to theinner substantially circular portion or from the inner substantiallycircular portion to the outer substantially circular portion, therebyconveying the fluid between the outer substantially circular portion andthe central portion. Since the ring pocket holding the fluid is sealedby the piezoelectric element itself, leakage of the fluid is minimized.The fluid within the pocket is steadily conveyed, and a high ejectionpressure is generated. Since the piezoelectric element has a disk shapeincluding the concentric segment electrodes, a simple and compactstructure is achieved.

The fluid conveyed by the fluid conveyance device according to apreferred embodiment of the present invention may preferably be a liquidor a gas (such as air). In particular, if the piezoelectric element isdriven at a high frequency, the fluid is preferably a gas. When air isused as the fluid, the fluid conveyance device may preferably be used asa cooling blower for semiconductor devices or a blower for evaporatingwater generated at an air electrode of a fuel cell. The amplitudes ofthe voltages applied to the segment electrodes need not necessarily beequal or substantially equal at all of the segment electrodes. However,if the amplitudes of the voltages are set to be equal or substantiallyequal to each other, the amount of displacement of each of the segmentelectrodes is set to be substantially equal. If the gaps between thesegment electrodes are radially arranged with an equal or substantiallyequal pitch, the volume of the pocket is changed at a substantiallyconstant rate, and the flow of the fluid is smooth.

Preferably, a first flow passage port is provided on the central portionof one of the substrate and the piezoelectric element, and a second flowpassage port is provided on the outer substantially circular portion ofone of the substrate and the piezoelectric element or between the outersubstantially circular portions of both of the substrate and thepiezoelectric element. The reversal of the phases of the voltagesapplied to the piezoelectric element switches between an operation ofsuctioning the fluid from the outer substantially circular portion andejecting the fluid from the central portion and an operation ofsuctioning the fluid from the central portion and ejecting the fluidfrom the outer substantially circular portion. More specifically, aswitching operation is preferably performed to switch between anoperation with the first flow passage port defining an outlet port andthe second flow passage port defining an inlet port and an operationwith the first flow passage port defining an inlet port and the secondflow passage port defining an outlet port. In particular, in theoperation with the fluid suctioned through the outer substantiallycircular portion and then ejected through the central portion, thepocket decreases in volume as the pocket moves from the outersubstantially circular portion to the central portion. Thus, an ejectionpressure is advantageously increased.

Preferably, the outer substantially circular portion of thepiezoelectric element is fixed to the substrate, and the first flowpassage port and the second flow passage port are closed by thepiezoelectric element and the substrate. Since the first flow passageport and the second flow passage port are closed with no voltageapplied, the flow of the fluid is stopped without using a valve.

The full surface of the piezoelectric element may preferably be incontact with the full surface of the substrate when no voltage isapplied to the piezoelectric element. In such a case, no pocket ispresent between the piezoelectric element and the substrate during a nodrive period, and the fluid is strongly suctioned and then stronglyejected even if the piezoelectric element is slightly displaced.

In a structure supporting the piezoelectric element on the substrate,the outer substantially circular portion of the piezoelectric elementmay preferably be fixed to the substrate or may preferably beelastically supported by the substrate. In the former case, the outersubstantially circular portion of the piezoelectric element ispreferably fixed to the substrate, and the piezoelectric element isprevented from lifting off of the substrate. The efficiency of the pumpis increased. In the latter case, the outer substantially circularportion of the piezoelectric element is bent, which causes a second flowpassage port between the piezoelectric element and the substrate. Thepiezoelectric element is not strongly bound and is thus free to bedisplaced. Any optional support structure may be applied to thepiezoelectric element.

The piezoelectric element is preferably a multilayer type having abimorph structure. For example, the piezoelectric element may be amultilayer type in which at least three circular or substantiallycircular concentric segment electrodes and a full-surface nonsegmentedelectrode are alternately laminated with a piezoelectric layerinterposed therebetween. The piezoelectric element may preferably be amultilayer type in which a plurality of first substantially circularconcentric segment electrodes and a plurality of second segmentelectrodes are alternately laminated with a piezoelectric layerinterposed therebetween, and wherein the second segment electrodes areconcentric with the first segment electrodes and gaps between the secondsegment electrodes are alternately arranged with a gap between the firstsegment electrodes in a radial direction. In the former case, oneelectrode is a full-surface electrode, and each of the electrodepatterns are the same type. The latter case provides the advantage thatthe number of segment electrodes on a surface is less than that of theformer case, and that the voltage applied to each segment electrode canbe reduced.

The segment electrodes arranged on the disk-shaped piezoelectric elementare not necessarily arranged to be substantially circular andconcentric. The plurality of segment electrodes may be successivelydeviated to one side. More specifically, if the diameter of thepiezoelectric element is reduced, the volume of the pocket formed in acircular shape is reduced in proportion to the diameter of thepiezoelectric element approximately to the fourth power. An ejectionamount of the fluid thus substantially decreases. In contrast, if theplurality of segment electrodes are successively deviated to one side,each segment electrode includes a wide portion and a narrow portion.With this arrangement, the volume of the pocket is maintained in thewide portion of the each segment electrode. Even if the diameter of thepiezoelectric element is decreased, the reduction of the volume of thepocket is minimized, and the reduction in the ejection amount is alsominimized.

If the height of the ridge line of the bending deformation is notuniform with the deviated segment electrodes, a clearance gap may openat the edge of the pocket, which leads to poor sealing. Thus, a requiredamount of flow and pressure of the fluid cannot be obtained. The borderline of each electrode must be determined so that the electrode patternshave a uniform ridge line height. For this reason, the border line ofthe electrode, i.e., the gap between the electrodes, is preferably setto be substantially proportional to the square root of a distance to animaginary straight line disposed on a circle outside the piezoelectricelement. In this case, lines connecting the imaginary straight line tothe peak of each pocket portion are aligned on a plane. Thus, eachpocket is reliably sealed, and the fluid can be reliably conveyed.

The piezoelectric element described above is arranged in a bendablemanner on the fixed substrate. The substrate may preferably be apiezoelectric element. More specifically, two disk-shaped piezoelectricelements are preferably arranged to face each other and be symmetricallydisplaced. In this case, the volume of the pocket is approximatelydoubled, which increases the ejection amount.

In accordance with a preferred embodiment of the present invention, thedisk-shaped piezoelectric element including the plurality ofsubstantially circular concentric segment electrodes is arranged on thesubstrate. The voltages are applied to the segment electrodes with thephase of the voltages being successively shifted. Thus, thepiezoelectric element is bent, which produces the ring pocket betweenthe piezoelectric element and the substrate. By moving the pocket in aradial direction, the fluid is radially conveyed. Since thepiezoelectric element has a disk shape, and the segment electrodes areconcentric or substantially concentric, the ring pocket holding thefluid is sealed with the piezoelectric element itself, and a highejection pressure is produced. Since the fluid conveyance deviceincludes the single disk-shaped piezoelectric element and the substrate,the device can be simple, compact, and thin. Furthermore, since the flowpassage between the inlet port and the outlet port is closed by the bentpiezoelectric element, check valves are not required for the inlet portand the outlet port.

Other features, elements, steps, characteristics and advantages of thepresent invention will become more apparent from the following detaileddescription of preferred embodiments of the present invention withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating a piezoelectric micro pump inaccordance with a first preferred embodiment of the present invention.

FIG. 2 is an exploded perspective view of the piezoelectric micro pumpillustrated in FIG. 1.

FIG. 3 is a sectional view taken along line III-III in FIG. 1.

FIG. 4 illustrates a cross section and a wiring of a piezoelectricelement for use in the piezoelectric micro pump illustrated in FIG. 1.

FIGS. 5A and 5B illustrate electrode patterns of the piezoelectricelement illustrated in FIG. 4.

FIG. 6 illustrates phases of voltages applied to the piezoelectricelement illustrated in FIG. 4.

FIG. 7 is an analysis diagram illustrating displacements of thepiezoelectric elements at each phase when the voltages illustrated inFIG. 6 are applied.

FIG. 8 illustrates a change in the volume of a central pocket with thevoltages illustrated in FIG. 6 applied.

FIGS. 9A to 9D are sectional views illustrating displacements of thepiezoelectric element with an outer substantially circular portion ofthe piezoelectric element fixed to a substrate.

FIG. 10 illustrates an example of the electrode structure that routes asegment electrode illustrated in FIG. 5 to the outside.

FIGS. 11A and 11B illustrate another example of the electrode structurethat routes the segment electrode illustrated in FIG. 5 to the outside.

FIGS. 12A and 12B illustrate electrode patterns of a piezoelectricelement in accordance with a second preferred embodiment of the presentinvention.

FIG. 13 illustrates a cross section and a wiring of the piezoelectricelement illustrated in FIG. 12.

FIG. 14 illustrates phases of voltages applied to the piezoelectricelement illustrated in FIG. 12.

FIGS. 15A and 15B illustrate an example of the electrode structure thatroutes the segment electrode illustrated in FIG. 12 to the outside.

FIGS. 16A and 16B illustrate another example of the electrode structurethat routes the segment electrode illustrated in FIG. 12 to the outside.

FIG. 17 illustrates an electrode pattern of a piezoelectric element inaccordance with a third preferred embodiment of the present invention.

FIG. 18 illustrates a design method of the electrode pattern of thepiezoelectric element illustrated in FIG. 17.

FIG. 19 illustrates a displacement of the piezoelectric elementillustrated in FIG. 17.

FIGS. 20A to 20D are sectional views of a displacement of apiezoelectric micro pump according to a fourth preferred embodiment ofthe present invention.

FIG. 21 is a sectional view of a piezoelectric micro pump according to afifth preferred embodiment of the present invention.

FIG. 22 is a sectional view of a piezoelectric micro pump according to asixth preferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the present invention are described below withreference to examples.

First Preferred Embodiment

FIGS. 1-3 illustrate a first preferred embodiment of a fluid conveyancedevice of the present invention. Here, the fluid conveyance device ispreferably used as an air supplying micro pump. FIG. 1 is a perspectiveview of the micro pump A of the first preferred embodiment, FIG. 2 is anexploded perspective view of the micro pump A, and FIG. 3 is a sectionalview taken along line III-III in FIG. 1.

The micro pump A of the first preferred embodiment includes a substrate10 defining a fixed plate, and a disk-shaped piezoelectric element 20arranged in a bendable manner on the substrate 10. An entire orsubstantially entire outer substantially circular portion of thepiezoelectric element 20 is preferably bonded to the piezoelectricelement 20 preferably by an adhesive agent 11, for example. Inaccordance with the first preferred embodiment, the substrate 10 and thepiezoelectric element 20 are preferably disks having the same orsubstantially the same diameter, for example. However, the substrate 10may have any optional shape and may be larger than the piezoelectricelement 20, for example. The substrate 10 is preferably a rigid metalplate or a resin plate, for example, and includes on the top portionthereof a planar material member that is in contact with thepiezoelectric element 20. A plurality of inlet ports 12 are preferablyprovided in a portion of the substrate 10 spaced inwardly from the outersubstantially circular portion at which the adhesive agent 11 isapplied. An outlet port 13 is preferably provided in a portion of thesubstrate 10 facing the approximate center of the piezoelectric element20. Alternatively, the inlet ports 12 and the outlet port 13 may beprovided on the piezoelectric element 20 instead of the substrate 10 orthe inlet ports 12 may be defined by grooves on the top surface of thesubstrate 10 that communicate with the outer substantially circularportion of the micro pump A. As illustrated in FIG. 3, preferably, theentire or substantially surface of the substrate 10 is in contact withthe entire or substantially the entire surface of the piezoelectricelement 20 when no voltage is applied to the piezoelectric element 20,and no pocket or cavity is provided therebetween and the inlet ports 12and the outlet port 13 are closed.

FIGS. 4, 5A, and 5B illustrate the detailed structure and the wiringstructure of the piezoelectric element 20. With reference to FIG. 4, thepiezoelectric element 20 includes two piezoelectric layers 21 a and 21 blaminated with a full-surface electrode 22 interposed therebetween. Thetwo piezoelectric layers 21 a and 21 b are preferably polarized in thesame direction as denoted by an arrow P. Preferably, five segmentelectrodes 23 a-23 e, for example, are split by narrow gaps G1-G4 andconcentrically arranged on the top and bottom main surfaces of thepiezoelectric element 20. The segment electrodes 23 a-23 e preferablyinclude the first substantially circular segment electrode 23 a arrangedin the approximate center of the piezoelectric element 20, and secondthrough fifth ring segment electrodes 23 b-23 e arranged to extendoutward from the first substantially circular segment electrode 23 a,for example. The first central segment electrode 23 a is connected tothe fifth segment electrode 23 e disposed in the outermost substantiallycircular potion. The segment electrodes 23 a-23 e on the bottom surfaceare similarly arranged. The segment electrodes facing each other on thetop and bottom surfaces are respectively connected each other, and arethen connected to a voltage application device 1. Referring to FIG. 4,the voltage application device 1 preferably applies a voltage E1 to thefirst and fifth segment electrodes 23 a and 23 e, a voltage E2 to thesecond segment electrodes 23 b, a voltage E3 to the third segmentelectrodes 23 c, and a voltage E4 to the fourth segment electrodes 23 d,for example. The full-surface electrode 22 is connected to the ground,i.e., to zero V.

In the first preferred embodiment, the gaps G1-G4 between the segmentelectrodes are preferably arranged in circles having the same orsubstantially the same pitch, for example. More specifically, asillustrated in FIG. 5A, where D represents a diameter D of the gap G1between the first segment electrode 23 a and the second segmentelectrode 23 b, the diameter of the gap G2 between the second segmentelectrode 23 b and the third segment electrode 23 c is 2D, the diameterof the gap G3 between the third segment electrode 23 c and the fourthsegment electrode 23 d is 3D, the diameter of the gap G4 between thefourth segment electrode 23 d and the fifth segment electrode 23 e is4D, and the external diameter of the fifth segment electrode 23 e, whichis the external diameter of the piezoelectric element 20, is 5D.

FIG. 6 illustrates amplitudes and phases of the voltages E1-E4 that thevoltage application device 1 applies respectively to the segmentelectrodes. With reference to FIG. 6, the sinusoidal wave voltages E1-E4that are different in phase by about 90 degrees and that have the sameor substantially the same amplitude are preferably applied. By applyingthe voltages that are different in phase by about 90 degrees, thedisplacements illustrated in FIG. 7 are generated on the piezoelectricelement 20. The voltages that are different in phase by 90 degrees arepreferably applied to the four segment electrodes, for example, in thefirst preferred embodiment. The phase may be changed depending on thenumber of segment electrodes. For example, voltages that are differentin phase by about 120 degrees may be applied to three segmentelectrodes, and voltages that are different in phase by about 60 degreesmay be applied to six segment electrodes, for example.

FIG. 7 illustrates simulation results of the displacement of eachportion of the piezoelectric element 20 with the outer substantiallycircular portion not being fixed. The piezoelectric element 20 used inthe simulation has a diameter of about 30 mm and a thickness of about0.3 mm, for example. The abscissa of FIG. 7 represents the position in aradial direction and the ordinate represents a displacement of bendingdeformation in a Z direction (height direction). The smallestdisplacements are substantially aligned with zero. Phases of sinusoidalwaves shifted in steps of about 45° are represented by t1-t8, and eightcurves represent the displacements when the voltages are applied to therespective electrodes with the phases thereof shifted by about 45°. Theposition at zero displacement is presumed to be at a facing surface,e.g., the substrate 10. The piezoelectric element is arranged to contactwith the floor surface at a diameter of about 12.5 mm slightly beyondphase t5, and a central contact point and a contact position arereversed. In this manner, a pocket holding the fluid appears at theapproximate center between the floor surface and the piezoelectricelement. The central pocket decreases in volume as time passes in theorder of t5-t6-t7-t8-t1-t2, and finally disappears.

FIG. 8 illustrates a change in the volume of the central pocket. It isunderstood from FIG. 8 that the volume of the central pocket decreasesat a substantially constant rate. If a hole 13 is opened at theapproximate center of the floor surface (the substrate 10), the fluidcan be ejected through the hole in the process of t5-t6-t7-t8-t1-t2-t3.In a subsequent process of t4-t5, the suction of a new fluid input fromthe outer substantially circular portion is completed. This process isrepeated hereinafter. By driving the piezoelectric element 20 with asufficient frequency, a large average ejection quantity is obtained,although with some fluctuation. The resonance frequency of thepiezoelectric element 20 of the first preferred embodiment is about 4kHz, and a frequency as high as possible but not above the resonancefrequency is preferably used.

FIGS. 9A to 9D illustrate an actual displacement of the piezoelectricelement 20 with the outer substantially circular portion being fixed.With the sinusoidal wave voltages E1-E4 that are different in phase byabout 90° and have the same or substantially the same amplitude applied,a wavy bending deformation occurs in a radial direction on thepiezoelectric element 20 and a pocket S having a ring shape is producedbetween the piezoelectric element 20 and the substrate 10 as illustratedin FIGS. 9A and 9D. The pocket S moves from the outer substantiallycircular portion to the central portion on the piezoelectric element 20.For this reason, the fluid is suctioned through the inlet ports 12 onthe outer substantially circular portion and then discharged through theoutlet port 13 on the central portion. FIG. 9A illustrates a state ofthe piezoelectric element 20 in which the ring pocket swell S isgenerated on the outer substantially circular portion. The fluid issuctioned through the inlet ports 12 and then enters the pocket S. FIG.9B illustrates a state of the piezoelectric element 20 in which the ringpocket S generated on the outer substantially circular portion movestoward an inner circle with the inlet ports 12 and the outlet port 13almost closed. In this state, the outer circle and the inner circle ofthe pocket S holding the fluid are sealed in response to the bending ofthe piezoelectric element 20, and an amount of leaks of the fluid isvery small. FIG. 9C illustrates a state of the piezoelectric element 20in which the pocket S further moves towards an inner circle until thepocket swell S is merged at the approximate center, and the ejection ofthe fluid through the outlet port 13 begins. FIG. 9D illustrates a stateof the piezoelectric element 20 in which the bending of thepiezoelectric element 20 moves further towards an inner circle until thedisplacement at the approximate center thereof is maximized. Thepiezoelectric element 20 returns to the state of FIG. 9A and theejection of the fluid through the outlet port 13 continues until thestate of FIG. 9A is resumed.

The micro pump A has the above-described structure that causes the fluidto be suctioned through the inlet ports 12 provided at the outersubstantially circular portion and ejects the fluid through the outletport 13 formed at the center portion. In this case, the ring pocket Sshifts from the outer substantially circular portion to the centralportion with the volume thereof gradually decreased, and then, causesthe fluid to eject through the outlet port 13 at the approximate centerin a burst. Therefore, the ejection pressure of the fluid that isejected through the outlet port 13 is increased. During non-drivingperiods, the surface of the piezoelectric element 20 remains in contactwith the surface of the substrate 10, and produces no pocket. If thepiezoelectric element 20 is slightly displaced, the fluid can besuctioned, and then can be ejected at a high pressure.

FIG. 10 illustrates an example of an electrode structure according to apreferred embodiment of the present invention that routes the segmentelectrodes 23 a-23 e provided on the top and bottom surfaces to theoutside. Referring to FIG. 10, an extension electrode 25 a extendingradially from the first segment electrode 23 a at the approximate centerto the outer circle edge is provided. Extension electrodes 25 b-25 dextending radially from the second-fourth segment electrodes 23 b-23 dand in parallel or substantially in parallel with the extensionelectrode 25 a to the outer circle edge are provided. The extensionelectrode 25 a extending from the first segment electrode 23 a ispreferably connected to the fifth segment electrode 23 e on the mainsurface. Alternatively, the extension electrode 25 a may preferably beseparated from the fifth segment electrode 23 e. The segment electrodes23 a-23 e on both of the top surface and the bottom surface extend tothe outer circle edge and can preferably be connected together by anedge electrode (not shown).

If the piezoelectric element 20 has a multi-layered structure,through-holes 26 a-26 f may preferably be used to connect the segmentelectrodes 23 a-23 e on the top and bottom surfaces as illustrated inFIGS. 11A and 11B, for example. The through-holes 26 a-26 e arethrough-holes respectively connecting the segment electrodes 23 a-23 eon the top surface to their counterpart segment electrodes on the bottomsurface, and the through-hole 26 f is a through-hole connecting thefull-surface electrodes. In this case, electrode extensions are requiredonly at the through-hole portion, and a deformation can be produced in ashape that is closer to an axial symmetrical shape.

If the piezoelectric micro pump A is arranged such that the outlet port13 faces a heat generating element (such as a semiconductor bare chip),air pushed out through the outlet port 13 can effectively cool the heatgenerating element. If the piezoelectric micro pump A is arranged toface an air electrode of a direct-methanol fuel cell, water generated atthe air electrode is evaporated and thus removed. The output of the fuelcell is increased thereby. In the case of a stacked fuel cell, a flowpassage may be arranged so that air pushed out through the outlet port13 flows between the cells, and water generated at the air electrode isevaporated and removed. The output of the fuel cell is increased.

Second Preferred Embodiment

FIGS. 12A-14 illustrates a second preferred embodiment of a fluidconveyance device of the present invention. Unlike the first preferredembodiment, the second preferred embodiment includes two differentpatterns as the segment electrodes of a piezoelectric element 30. Withthe diameter of the piezoelectric element 30 being 5D, a first electrodepattern includes three concentric substantially circular segmentelectrodes 32 a-32 c divided along a diameter D and a diameter 3D asillustrated in FIG. 12A, and a second electrode pattern includes threeconcentric substantially circular segment electrodes 33 a-33 c dividedalong a diameter 2D and a diameter 4D as illustrated in FIG. 12B.

As illustrated in FIG. 13, two types of segment electrodes 32 a-32 c and33 a-33 c are preferably laminated with piezoelectric layers 31 a and 31b interposed therebetween. The segment electrodes 32 a at theapproximate center are mutually connected to the outermost segmentelectrodes 32 c, and the segment electrodes on the top surface arerespectively connected the segment electrodes on the bottom surface. Theinterlayer segment electrodes 33 a and 33 c are connected to each otherand an extension therefrom is routed to the outside. The interlayersegment electrode 33 b is preferably separately routed to the outside. Avoltage application device that is not illustrated applies a voltage e1to the segment electrodes 32 a and 32 c, a voltage e2 to the segmentelectrodes 33 a and 33 c, a voltage e3 to the segment electrode 32 b,and a voltage e4 to the segment electrode 33 b. FIG. 13 illustrates anexample in which the first electrode pattern 32 a-32 c defines the mainsurface electrodes, and the second electrode pattern 33 a-33 c definesas the interlayer electrodes. Alternatively, the first electrode pattern32 a-32 c may define the interlayer electrodes, and the second electrodepattern 33 a-33 c may define the main surface electrodes.

FIG. 14 illustrates the amplitude and phases of the voltage e1-e4applied to the segment electrodes. As illustrated in FIG. 14, thesinusoidal wave voltages e1-e4 that are different from each other inphase by about 90 degrees and that have the same amplitude are appliedto the segment electrodes, and a displacement similar to thedisplacement illustrated in FIG. 7 is produced on the piezoelectricelement 30. In the first preferred embodiment, the voltages E1-E4 havingphases that are shifted by about 90 degrees one from another are appliedbetween the segment electrodes 23 a-23 e and the full-surface electrode22 (0 V). In the second preferred embodiment, the voltages e1-e4 havingthe phases that are shifted by about 90 degrees from one another areapplied between the segment electrodes facing each other with thepiezoelectric layer interposed therebetween. Even with voltages e1-e4having smaller amplitudes than the voltages E1-E4, the same orsubstantially the same displacement amounts are produced. The number ofsegment electrodes provided on one surface is less than in the firstpreferred embodiment. In other words, the number of gaps defining thesegment electrodes is reduced, and the piezoelectric element 30 iseffectively bent.

FIGS. 15A and 15B illustrate an example of a structure that is providedto extend the segment electrode on the piezoelectric element 30 of thesecond preferred embodiment. Referring to FIG. 15A, the central segmentelectrode 32 a and the segment electrode 32 c on an outer substantiallycircular portion are connected to each other by an extension electrode35 a extending in a radial direction. Moreover, the intermediate segmentelectrode 32 b is routed to an outer substantially circular edge via anextension electrode 35 b. Referring to FIG. 15B, the central segmentelectrode 33 a and the segment electrode 33 c on an outer substantiallycircular portion are connected to each other by an extension electrode36 a extending in a radial direction. The intermediate segment electrode33 b is thus routed to an outer substantially circular edge via anextension electrode 36 b extending in a radial direction. The extensionelectrodes 35 a and 35 b and the extension electrodes 36 a and 36 b arepreferably arranged in perpendicular or substantially perpendiculardirections, for example, so that the extension electrodes do not crosseach other. The electrodes that extend to the outer substantiallycircular edge are preferably connected by an edge electrode (not shown),for example.

FIGS. 16A and 16B illustrate the piezoelectric element 30 in whichthrough-holes are provided instead of the extension electrodes in aradial direction and the edge electrode illustrated in FIGS. 15A and15B. More specifically, the first electrode patterns 32 a-32 c arerespectively connected to each other and the second electrode patterns33 a-33 c are respectively connected to each other by the though-holes37 a-37 f. In this case, electrode extensions are required only at thethrough-hole portion, and the deformation that is produced canpreferably have a shape closer to an axial symmetrical shape.

Third Preferred Embodiment

FIGS. 17-19 illustrate a third preferred embodiment of the fluidconveyance device of the present invention. In accordance with the thirdpreferred embodiment, the electrode patterns of a piezoelectric element40 are not concentric, but are arranged in a deviated arrangement asillustrated in FIG. 17. More specifically, ring segment electrodes 41b-41 e are successively arranged around a central segment electrode 41 ain an arrangement that is not centered. A pitch of the gaps G4-G4defining border lines between the segment electrodes is set tosubstantially proportional to the square root of a distance to animaginary straight line O, shown in FIG. 19, outside the piezoelectricelement 40. In this preferred embodiment, the imaginary straight line Ois x=0 (Y axis in FIG. 18). The border line pitch is preferably set tobe about 0.8x^(0.5), for example, so that the pitch is substantiallyproportional to the square root of a distance x from the imaginarystraight line O. If the diameter of the piezoelectric element 40 isabout 30 mm, for example, the center of the piezoelectric element 40 is(x,y)=(17,0).

A displacement height h is approximately proportional to the square ofthe border line pitch (pitch of the gaps G1-G4) during deformation.Therefore, the volume of the pocket holding the air is increased to agreater extend when the electrodes are arranged in a deviated mannerthan when the electrodes are concentrically arranged. For this reason,the deviated electrodes are more advantageous to increase the amount offlow of the fluid. However, if the height of the ridge of thedeformation is not uniform, a clearance gap may be opened at the edge ofthe pocket. As a result, the device may suffer from poor sealing and maylack a flow amount and pressure. Thus, the border line needs to bedetermined so that an electrode pattern that results in a uniform heightof the ridge of the pocket is provided.

The displacement height h of the deformation is approximatelyproportional to the square of the border line pitch. If the border linepitch is set to be proportional to the square root of the distance fromthe imaginary straight line O outside the piezoelectric element, theheight of the ridge is aligned substantially in a single plane. If theborder line pitch is selected as illustrated in FIG. 19 so that theborder line pitch is proportional to the square root of the distance xfrom the imaginary straight line O, a pocket pitch δx is substantiallyproportional to the border line pitch. The pocket pitch δx is alsosubstantially proportional to the square root of the distance x from theimaginary straight line O as below.δx∝x^(0.5)where the pocket height is proportional to the square of the pocketpitch, the pocket height is proportional to the distance from theimaginary straight line O as below.h∝δx²∝x

A specific formation method of the segment electrodes 41 b-41 e isdescribed below. Referring to FIG. 18, a circle C1 defining an outerdiameter of the piezoelectric element 40 is first drawn. An approximatecircle C2 is next drawn by connecting points on lines drawnperpendicular to each point on the circle C1, the points to be connectedbeing located at 0.8x^(0.5) of the extension of each normal line insidethe circle C1. In a similar process, approximate circles C3, C4 and C5are drawn. The shapes of the segment electrodes 41 b-41 e are thusdetermined.

Fourth Preferred Embodiment

FIGS. 20A to 20D illustrate a piezoelectric micro pump B in accordancewith a fourth preferred embodiment of the present invention. In thefirst to third preferred embodiments, the piezoelectric element ispreferably arranged to face the substrate which is a fixed plate. In thefourth preferred embodiment, two piezoelectric elements 50 and 60 arearranged so as to face each other. In this preferred embodiment, outersubstantially circular portions of the piezoelectric elements 50 and 60are bonded together. The piezoelectric element 50 includes at theapproximate center thereof an outlet hole 51 and the piezoelectricelement 60 includes inlet holes 61 on the outer substantially circularportion thereof. The piezoelectric micro pump B preferably suctions thefluid from the bottom side thereof and ejects the fluid through thecenter of the top side thereof. In this case, the volume of the pocket Sholding the fluid is about twice as large as the volume that is producedwhen the fixed plate provided. Thus, the amount of flow of the fluid isadvantageously increased. Alternatively, both the inlet hole and theoutlet hole may be arranged on one of the piezoelectric element 50 andthe piezoelectric element 60.

Fifth Preferred Embodiment

FIG. 21 illustrates a piezoelectric micro pump C according to a fifthpreferred embodiment of the present invention. Similar to the firstpreferred embodiment, the fifth preferred embodiment includes thepiezoelectric element 20 with the outer substantially circular portionthereof being bonded to the substrate 10 preferably with the adhesiveagent 11, for example. During a no-voltage application period(non-driving period) of the piezoelectric element 20, the surface of thepiezoelectric element 20 is not entirely in contact with the substrate10, and a gap 14 is provided between the substrate 10 and thepiezoelectric element 20 in an area other than flow passage ports 12 and13 of the substrate 10. The height H of the gap 14 is less than theamplitude of the piezoelectric element 20. During the no-voltageapplication period, the piezoelectric element 20 is in contact with ringvalve seats 12 a and 13 a that surround the flow passage ports 12 and13, and the surface pressure acting on the ring valve seats 12 a and 13a is increased. Sealing performance of the flow passage ports 12 and 13is thus increased. In addition, in this preferred embodiment, the heightof the gap 14 is less than the amplitude of the piezoelectric element20, and the fluid is suctioned and ejected at high pressure.

Sixth Preferred Embodiment

FIG. 22 illustrates a piezoelectric micro pump D according to a sixthpreferred embodiment of the present invention. In the sixth preferredembodiment, a holder 14 is provided on the substrate 10. Elastic members15 elastically bias the outer substantially circular portion of thepiezoelectric element 20 against the substrate 10. In this case, theouter substantially circular portion of the piezoelectric element 20 isnot rigidly fixed to the substrate 10, and the edge of the outersubstantially circular portion of the piezoelectric element 20 is alsodisplaceable. For this reason, the amount of fluid that can be suctionedalong the outer substantially circular portion of the piezoelectricelement 20 and ejected is increased.

The above-described preferred embodiments preferably have a multilayerstructure in which two piezoelectric layers are laminated as apiezoelectric element. Alternatively, three or more piezoelectric layersmay be laminated. The use of a large number of thin layers enables alower application voltage to be used.

A multilayer structure is preferably produced by firing eachpiezoelectric layer having a single layer structure, forming electrodeson the top and bottom surfaces of each piezoelectric layer, and thenbonding the piezoelectric layers together. Another multilayer structureis produced by laminating a plurality of ceramic green sheets, eachhaving electrodes, and then firing the laminate.

According to the above-described preferred embodiments, the fluidconveyance device of the present invention is preferably applied as amicro pump to convey a compressible fluid, such as the air, for example.The fluid conveyance device may preferably be applied to anoncompressible fluid, such as a liquid, for example.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. A fluid conveyance device comprising: a substrate made of a rigidmaterial; and a disk-shaped piezoelectric element arranged in a bendablemanner on the substrate; wherein a plurality of substantially circularconcentric segment electrodes are provided on the piezoelectric element;a voltage application device is arranged to apply voltages to thesegment electrodes such that the voltages are successively shifted inphase; the voltages are applied to the segment electrodes with thephases thereof shifted so as to produce a wavy ring deformation on thepiezoelectric element and to move a pocket that is produced between thepiezoelectric element and the substrate in a radial direction such thata fluid is conveyed between an outer substantially circular portion anda central portion of the substrate; the disk-shaped piezoelectricelement is directly bonded to the substrate along only an outersubstantially circular portion of the disk-shaped piezoelectric element;a first flow passage port is provided on the central portion of one ofthe substrate and the piezoelectric element; a second flow passage portis provided on the outer substantially circular portion of one of thesubstrate and the piezoelectric element or between the outersubstantially circular portions of both of the substrate and thepiezoelectric element; the first flow passage port and the second flowpassage port are closed by the piezoelectric element and the substratewhen no voltages are applied to the piezoelectric element; and thepiezoelectric element and the substrate are in contact with one anotherat a periphery of the substrate.
 2. The fluid conveyance deviceaccording to claim 1, wherein substantially an entire surface of thepiezoelectric element is in contact with substantially an entire surfaceof the substrate when no voltages are applied to the piezoelectricelement.
 3. The fluid conveyance device according to claim 1, whereinthe piezoelectric element is a multilayer element in which at leastthree substantially circular concentric segment electrodes and afull-surface nonsegmented electrode are alternately arranged with apiezoelectric layer interposed therebetween.
 4. The fluid conveyancedevice according to claim 1, wherein the piezoelectric element is amultilayer element in which a plurality of first substantially circularconcentric segment electrodes and a plurality of second segmentelectrodes are alternately arranged with a piezoelectric layerinterposed therebetween; and the second segment electrodes aresubstantially concentric with the first segment electrodes and gapsbetween the second segment electrodes are alternately arranged in theradial direction with a gap between the first segment electrodes.
 5. Thefluid conveyance device according to claim 1, wherein the substrate isdefined by another piezoelectric element having a same structure as thepiezoelectric element; and voltages having substantially the same phaseare applied to the segment electrodes facing each other on thepiezoelectric element and the another piezoelectric element with thephase of the voltage successively shifted so as to symmetrically producethe ring wavy deformation on the piezoelectric element and the anotherpiezoelectric element and move the pocket that is produced between thepiezoelectric element and the another piezoelectric element in theradial direction such that the fluid is conveyed.